1. Field of the Invention
This invention relates to fluorometers and, more particularly, to a fluorometer which detects radiation emitted by a sample in response to a small area of light striking the sample.
2. Description of the Prior Art
Fluorometers have been widely adopted in laboratory and clinical analysis to identify and study the behavior of numerous materials and biological substances. A fluorescent sample absorbs light of a given wavelength and, in response thereto, emits light of a different wavelength. Often the efficiency of absorption and emission is low so that fluorometers of increasing sensitivity to emitted radiation are required for reliable analysis. As sensitivity is increased, however, the probability also increases that radiation from extraneous sources or from the excitation source will adversely affect detection of the radiation issuing from the sample.
Presently available fluorometers, which flood a sample using an ultraviolet source or which image a slit of light of a desired bandwidth on the sample, either lack the versatility to collect and detect the desired fluorescent radiation to the exclusion of radiation from other sources or are so complex and expensive in construction as to be impractical for many purposes. In this regard, by flooding a sample with ultraviolet light, all flourescent materials in the vicinity of the sample, such as nearby samples or extraneous materials, will fluoresce. As a result, extensive light baffling and shielding is employed to prevent this unwanted radiation from reaching the detector. Imaging a slit of light of a desired bandwidth on the sample in the past has involved complex arrangements of dispersive elements, such as optical prisms or gratings, which generally result in relatively low excitation energy levels and thus require more powerful radiation sources. Moreover, in both of the above approaches, in order to minimize entry of stray light into the system and to increase the system sensitivity to emitted radiation, the detector is either placed adjacent the sample being analyzed or is remotely located only if a complex optical system is employed between the sample and the detector.